Instrument shunt



W. A. ATWOOD INSTRUMENT SHUNT Jan. 11 1927.

Filed April 9 1925 Inventor Winfield AAtUJood Page.

His Attorneg Patented Jan. 11, 1927.

UNITED STATES PATENT OFFICE.

WINFIELD A. ATWOOD, OF SCHENECTADY, NEW YORK7 ASSIGNOR TO GENERAL ELEC-TRIC COMPANY, AA CORPORATION OF NEV YORK.

INSTRUMENT SHUNT.

Application filed April 9, 1925.

My invention relates to instrument shunts ot the type adapted to beinserted in an electric circuit so :is to shunt a definite portion oftthe emrent flowingtherethrough to an instrument or other device which isto be responsive to the line current.

As usually constructed. instrument shunts are nnnle ot' copper, or of amaterial containing a Vlarge percentage ol copper, in order to make theten'iperature coellieient ot resistance zero, or very lou'. Thetemperature coefficient o' resistance ot such a shunt is .fixed and isnot subject to adjustment for diil'erent instruments. .l'lig'h capacitycopper shunts having; the requisite resistance drop tl'iereaeross andthe heat dissil'iatiner capacity necessary toi' continuous heavy serviceare relatively expensive.

The object of my invention is to provide a rugged, relativelyinexpensive shunt arranged so that its teuiperature Coellieient ofresistance may be readily ndi usted to accommodate different instrumentsor other devices.

ln carrying my invention into e'lt'eet I provide a shunt made up ofirelatively inexpensive materials having different temperaturecoetlieients oi resistance, the tuo ninlerials being;- so arranged thatthe line eurrent 'lous in parallel therethrough and7 so that therelative resistance e'lii'ects of the differentmsterizilL-i may headjusted with respect to erich other and in this Way obtain a` desiredresultant temperature coeliioient ot resistance.

ln the construction olf my shunt, lY prefer to use cast iron and carbonsince these maiterials are relatively iilexpensive and have oppositetemperature coeliicients ol resistance. rl`he preterred constructiontakes the forni of corrugated cast iron Casing enclosing en adjustablestack ot' carbon discs so arranged that the current flowing through theshunt flows in parallel through thes/ inaterials. By adjusting therelative resistances ot these tu'o paths the temperature coeliiciei'itof resistance of the shunt may be changed. rl`he features ot myinvention which are believed to be novel und pateutable will be pointedout in the claims appended hereto. For u better understanding` ot inyinvention, reterence is made in the following description to theaccompunyin;v drawing in which Fig. l represents a side view, partiallyin SeraL No. 22,001.

ted :1t 'l-l and contains one or more 's l preterahly ot carbon, orother niaterial hevinn similar properties, compressed between adir teblenuts 15. The adjusting nuts are preierebly made secure by loch nuts 1G.Tivo or more shunt lend terminal bolt holes, reg'nresented at 1.7, 18,19, 20 and 21, nre provided 'to attach the leads which connect with themeinen-ing instrument or other device used with the shunt. It `vill beevident that this shunt is relatively inexpensive, both as to the costoit' the materials used and the mechanical operations necessary ttor itsconstruction. n

Cast iron has :L ]'i sitive teu'iperature coeli'ieient ot resistanceand, consequently, would not be suitable as :i snunt it used alone.Carbon, on the othei` hand, has a. negative temperature coellicient olresistance and likewise is not suitable for this purpose. However, bythe proper combination of these materials in parallel, a desirablecompromise temperature coetlicient may be obtained which, as will bemore fully explained hereinafter, may readily he altered to suitditierent instriunents. Cast iron and carbon both have positivetemperature coefficients of expansion7 that of a suitable grade ofcarbon being somewhat higher than that ot cast iron. It Will thereforebe'evident that es the shunt heats up, the castiron will estpand at nslightly less rate than the carbon discs 14, and this action willcompress the carbon discs and decrezise the resistance therethrough.This has the saine effect on the characteristics ot the shunt as thenegative temperature coefficient o resistance olf the carbon has. Theline current in flowing through the shunt Will pass entirely through theeast iron portion except that portion lying between the two sets of nutsl5 and 16.

lili',

llet-ween these points part ot' the current will flow through the carbondiscs. lt n'ill therefore be evident that to obtain a shunt ha vingi` azero temperature coefficient ot resist` ance across the extremeJ shuntterminals 17 and lts. the resultant teniperature e( etlicient oiresistance ot that portion oi' the shunt havingl the iron and carbonconnected in parallel must be negative te malte up Vt'or positivetemperature coetticient ot resistance otl the remaining' portion o t theshunt which is entirely otiren. 'there are a varietyv o t" ways in whichto change the resultant tenuperature cocllicient et the shunt betweenthe shunt terminals. AFor exampleT thc mnnher` thirliness or diameter otthe carbon discs ma),v be changed and one ot' the discs has beenrepresented as being thinner and ot a l 'i eter than the others tor thispuril slight. adjustment may also be had by tight enini;l or looseningthe clamping' nuts which compress the carbon discs. lt: will also beevident that tor any given iuljustnient the temperature coeliicient ofresi .ance across terminals 17 and 1S will be different than that acrossterminals 18 and 19, since that portion ot the shunt between terminals1T and 19 is entirely positive. Any ot these changes wil also change thevoltage drop across any set ot' terminals tor a `given line current andtemperature. The manner of adjustingthe shunt 't'or a given temperaturecoetiicient ot resistance and voltage drop will be clearer by taking;` aspecitie case. Suppose it is desired to provide a shunt having a Zeroten'iperature coetiicient ot resistance and a 1 volt drop for 100()amperes line current. rl`he shunt will be constructed with the generalproportions calculated to give this result. Suppose that when assembled.as illustrated in 1, the shunt gives 2.1 volts across terminals 17 and1S and has a temperature coefficient which is slightly negative. it willappear that to correct the temperature coefficient, We must reduce theeli'ect ot the carbon path and this will increase the total drop acrossthe shunt. Con sequently, it will be necessary7 to use shunt terminals18 and 21 or possibly 1S and 2t). The ettectot the carbon path may bereduced by reducing' its length or increasingV its resistance. A slightloosening` ot one set ot' nuts maybe sutiicient. It not. a disc may be.removed entirely or replaced by one ot less thickness or less diameterand the nuts again screwed down to the proper tension. rl`he twoconditions to be met must be considered together but by providing' asullicient number o'l shunt terminals oi slightly ditl'erent spacing` asrepresented at 1S), 20, 2l. and 1i' and a suitable variety oit extra'arbon discs these conditions may be met, The various carbon discs willpreferably be marked or otherwise identiiied and the shunt terminalsmarked so that after the shunt is reifer-:'42

once calibrated, a calilnatiim record may lic prepared and used tofacilitate obtaining the same or other desiredadjustments.

lt will be seen that ditlercnt terminals ot' this shunt may be used tosimultaneousljl obtain voltage drops proportional to the line currenthaving slightly dilt'erent resistance temperature coeticienteluuracteristic rl`hus, the same shunt may be simultaneously used tooperate an instrument having` a Zero temperature coetticient ot.resistance and a rela),v having a positive ten'iperature coctiicient etresistance.

l do not Wish to limit my invention to cast iron and carbon as thematerials to he used7 nor do l wish to limit. my invention to ma terialswhich have diti'erenttemj'veraturc cocliicients ot expansion, since itwill he evident that there are various grades ot iron and steel as wellas various grades ot carbon and substitutes tor carbon which may becombined in accordance with the tcachings ot this invention to obtainthe beneficial result thereof. tither miuiitications will occur Vtothose skilled in the art and.y consequently? I do not wish to be limitedte the particular embodiment ot my invention herein described, butintend to cover in the appended claims all modifications and embodimentscoming within the true spirit and scope of my invention.

llllzat l claim as new and desire to secure b v Letters `Patent ot theUnited States, is:-

t. .-\n electric shunt comj'nising` a conducting?Y member having` apositive temperature coetiicienti ot resistance, a conilucting` memberhaving' a negative temperature coelicient ol resistance connected inparallel with a portion ot the first mentioned memter, and shunt leadterminals adjacent the extremities of said shunt, said conductingmembers having their relative resistances adjusted so as to produce asubstantially zero temperature eoei'iicient ot resistance characteristicacross said shunt lead terminails.

An electric shunt comprising a conductor haring a given temperaturecoeflicicnt ot resistance, means tor securing' line connections to theextreniities ot said conductor, shunt lead terminals adjacent theextremities ot said conductor, a second comluctor having' a temperaturecoetiicient ol resist.- ance opposite to that' ol the lirst mentionedconi'luctor and conncctial in parallel with said irst mentionedcomluctor between the extremities thereof, and means t'or adjustingr theresistance ot said second mentioned condnctor.

il. )in electric shunt', comprising` a concluetor having a positivetemperature coetiicient' resistance. means 'tor securing lineconnections to the extremities thereot, shunt lead terminals adjacentthe extremities of said conductor and an adjustable carbon pile conllt)nccted in parallel. with a portion of said conductor.

el. An electric shunt having parallel connected conductor circuits ot"positive and negative temperature coelicients of resistancerespectively, and means tor adjusting the relative resistance etllectsof said parallel. connected circuit.

An electric shunt comprising a conductor having a positive teniperat-urecoefficient olE ref- .istance` line terminals therefor, shunt leadteri'uinals adjacent said line terminals, a conductor having' a negativeten'iperature coetticicntot resistance connected in parallel with a,portion oit said lirst mentioned conductor, und means tor adjustingthelength otl the parallel connected portions ot said conductors.

o. An electric shunt comprising' a castiron men'iher ha 'ing' an openingthrough one axis thereoli` line terminals and shunt lead terminalsadjacent the extremities ot' such axis, a carbon pile in said openingelectrically connected in parallel with the adjacent portion ol' saidcast-iron member, and means tor adjusting the length and the compressionot' said carbon pile.

7. An electric shunt comprising a corrugated cast-iron member having acylindrical opening' through one axis thereof, line terminals and shuntlead terminals adjacent the extremities et such axis, nuts threaded insaid opening and a carbon pile compressed between said nuts.

8. An electric shunt having line terminals, diti'erent portions et saidshunt between said line terminals having ditferent ten'iperaturecoetiicients ot resistance and means tor connecting` shunt leads across.different portions o't' said shunt so as to obtain a desired resultanttemperature coetlieient ot resistance characteristic.

9. An electric shunt having line terminals, ditlerent portions ot saidshunt between said line terminals havingdi t'lerent temperaturecoetlicients ot resistance, means for varying' the temperatureeoetlicients et resistance et one portion ot said shunt, and means torconnectingshunt leads across different portions ot said shunt whereby adesired voltage drop and temperature coellicients ot resistanceclnuacteristic may he obtained.

l0. An electric shunt comprising parallel comluctors having differenttemperature coeticients ot expansion and opposite temperatureeoei'i'icieiits of resistance secured in lixed relation with each other.

AIn witness whereof, I have hereunto set my hand this 8th day of April,1.925.

W'INFIELD A. ATVGOD.

